Electromagnetic clutch-brake system



Dec. 14, 1965 F. H. SHEPARD, JR 3,223,212

ELECTROMAGNETIC CLUTCH-BRAKE SYSTEM Filed Aug. 21. 1961 VENTOR 75 7d Aka/0r Iii $1 4 64 .73

BY @052 WW g gW S 3,223,212 ELECTROMAGNETIC CLUTCH-BRAKE SYSTEM Francis H. Shepard, .lr., Lee Lane, Berkeley Heights, NJ. Filed Aug. 21, 1961, Ser. No. 132,684 6 Claims. (Cl. 192-18) This invention relates to an electromagnetic clutchbrake system.

An object of this invention is to provide a clutch or brake system which operates at higher speed than previous systems.

A further object is to provide such system which operates with greater efficiency.

Still another object is to provide an improved clutchbrake unit for precisely and at high speed controlling the driving of a shaft.

These and other objects will in part be understood from and in part pointed out in the description given hereinafter.

In the inventors US. Patent No. 2,924,314 there is disclosed a very effective electromagnetic clutch-brake unit and energizing circuit. This arrangement is particularly suitable for driving and stopping the paper shift mechanism in a high speed printer, such as described in the inventors US. Patent No. 2,787,210. Now, such a printer is capable of printing at a tremendous rate of the order of 200,000 characters a minute. But to do this requires feeding a strip of paper through the machine, starting and stopping the paper in some instances at a rate of about 60 lines a second. This imposes strenuous requirements on the mechanism for driving the paper.

Ideally, a clutch-brake unit for this purpose should be able to go from stop to full speed, and vice versa, instantaneously so that the paper can be shifted from one line to the next in minimum time. But because of several factors, including the inertia of elements of the system, some delay in starting or stopping occurs. The present invention achieves a very sizeable reduction in this delay, reducing it to only a few thousandths of a second.

In accordance with the present invention, in one specific embodiment thereof, a brake electromagnet coil and a clutch electromagnet coil, similar to the ones disclosed in the above mentioned patent, are positioned on opposite sides of a rotatable disc which carries in its face magnetic clutch elements. These coils are then energized alternately with electric current so that when one coil is on the other is off, and vice versa. This causes the clutch elements to be attracted to one, then the other coil, thereby driving or stopping an output shaft on which the rotatable disc is fixed. Now when the current to one coil is turned off and current to the other is turned on, instead of merely allowing the current to die out to zero in the first coil, this current is caused very quickly to drop to zero and then reverse. The effect of this is to cause the magnetism of the coil much more quickly to drop to zero and then actually reverse in polarity. At the same time, of course, the magnetism in the other coil is building up and so the clutch elements are spit off from the first coil toward the other. 1 By this means the time of moving the clutch elements from one coil over to the other, or vice versa, is greatly reduced.

The actual details of this arrangement together with other features of the invention will best be gained from 3,223,212 Patented Dec. 14, 1965 the following description given in connection with the accompanying drawings wherein:

FIGURE 1 shows a clutch-brake system embodying features of the invention; the clutch-brake unit being shown in exploded relation;

FIGURE 2 is a representation of velocity and voltage waveforms of the system; and

FIGURE 3 is an enlarged cross-section view of a portion of the clutch-brake unit.

The system 10 shown in FIGURE 1 comprises a clutch-brake unit 12, shown in exploded relation, and an associated current supply circuit generally indicated at 14. The clutch-brake unit includes a clutch electromagnet 16 which is supported on bearings (not shown) and is adapted to be rotated at a constant speed by a drive motor (not shown). The right-hand face of this electromagnet, see also FIGURE 3, is formed by two annular rings 18 and 20, which lie in the same plane, and which are separated by an annular gap 22. These rings are advantageously of hardened steel, magnetic and wear resistant. When electromagnet 16 is energized by a unidirectional current, a unidirectional magnetic field appears across gap 22.

Passing freely through the center of electromagnet 16, is a shaft 24, which is rotatably supported in bearings (not shown) and to which is fixed a disc 26. The latter, as seen in FIGURE 3, is positioned immediately in front of electromagnet 16. This disc is non-magnetic and has wedge-shaped holes cut through it in which respective ones of four magnetic clutch elements 28 are loosely fitted. When, for example, electromagnet 16 is on, these clutch elements will be pulled onto rings 18 and 20 thereby establishing a driving connection between the electromagnet and shaft 24.

Positioned on the other side of disc 26 is a brake electromagnet 30. This, as with clutch electromagnet 16, has annular face rings 32 and 34 separated by a gap 36. Shaft 24- passes freely through this electromagnet also.

As seen in FIGURE 3, each clutch element has a soft iron core 40 on the outer faces of which are coated brake lining material 42. When first placed in the unit, the iron core extends at 44 on each side beyond the vertical plane of the brake lining. It will be noted that portions 44 slightly more than cover gaps 22 and 36. Now, after the unit has been operated for a short while, portions 44 are worn down, as indicated by the dotted lines 46, so that the bare and the brake lining on each side of a clutch element form a plane face exactly conforming to the face of the adjacent electromagnet. Because when one or the other electromagnet is on, the bare iron of the clutch elements is in intimate, direct contact with rings 18 and 20, or rings 32 and 34, and bridges gap 22 or 36, the force with which the clutch elements are held is maximized.

As seen in FIGURE 1, the electromagnets are energized alternately by circuit 14. This includes a first output transistor 50 and a second output: transistor 52. When the first of these is on the other is off, and vice versa. The emitters of transistors 50 and 52 are connected in common through a silicon diode 54 to the positive side of a battery 56. The collector of transistor 50 is connected through a low ohmage resistor 60 to one side of the winding of clutch electromagnet 16, the other side of this winding being connected to the negative side of battery 56. Shunting resistor 60 is a large capacitor 62.

When transistor 50 is suddenly turned on, a pulse of voltage having a sharp leading edge indicated by waveform 64 in FIGURE 2, is applied to electromagnet 16 and this causes shaft 24 to be driven. This electromagnet is energized for as long as needed to drive shaft 24 a required distance. Then transistor 50 is turned off and transistor 52 turned on; When transistor 50 is turned off, a path back through capacitor 62, and a second capacitor 66, bypassing transistor 50, provides a damped resonant discharge circuit for the current then flowing in electromagnet 16. This causes the current to very rapidly decay and to reverse in the electromagnet. The capacitor 66 limits the amplitude of the kickback voltage across electromagnet 16, as indicated by the negative spike 68 in FIGURE 2, and provides a reverse current to the electromagnet. Of course, at the same time that the current in clutch electromagnet 16 is turned off and reverses, the brake electromagnet is turned on as indicated by the dotted voltage waveform 70 in FIGURE 2. This causes very rapid shifting of clutch elements 28 from contact with the clutch to the brake electromagnet.

Transistor 52 is similarly connected through a low ohmage resistor 72 shunted by a large capacitor 74 to the winding of brake electromagnet 30. A resonant discharge path is provided through capacitor 74 and a capacitor 76 shunting transistor 52. Thus whenever the latter is turned off, the current in brake electromagnet 30 will reverse, as indicated in FIGURE 2 by the dotted voltage spikes 78.

Current is applied to clutch electromagnet 16 in the sense so that ring 18 becomes a north pole (N) and ring a south pole (S), for example. Similarly, current when applied is applied to brake electromagnet in the sense so that ring 32 becomes a north pole and ring 34 a south pole. Now, the clutch elements 28 are highly magnetic and when the clutch electromagnet is on, they will be held with great force bridging the gap across rings 18 and 20. When the current in this electromagnet reverses, ring 18 which had been a north pole, reverses and becomes a south pole and ring 20 becomes a north pole. But the clutch elements, having been strongly magnetized by their intimate contact with rings 18 and 20, will have some residual magnetism (which is being supported by flux from the now on brake electromagnet 30) so that now they will be repelled from rings 18 and 20, and of course at the same time strongly attracted toward rings 32 and 34 of the brake electromagnet. Thus the time delay going from stop to full speed in the driving of shaft 24 as indicated in FIGURE 2 by waveform 80 is reduced to about 4 milliseconds which is less than half that obtained in previous systems.

As seen in FIGURE 1, the base of transistor is connected to the emitter of a driver transistor 82. This emitter is connected through a moderately low ohmage resistor 84 to the positive side of battery 56, and the collector of transistor 82 is connected through a low ohmage resistor 86 to the negative side of battery 56. When driver transistor 82 is off, output transistor 50 is oif and output transistor 52 is on. When driver transistor 82 on, the base of transistor 50 is driven negative and it is thus turned on. However, the voltage drop across resistor 86, when driver transistor 82 is on, is sufiicient in conjunction with the forward voltage drop across diode 54 to turn transistor 52 fully off. The base of transistor 52 is connected through a moderately low ohmage resistor 88 to the positive side of battery 56 and through a silicon diode 90 to resistor 86. When driver transistor 82 is off, transistor 52 is biased on.

Driver transistor 82 is controlled by a signal from the output of a flip-flop unit 92 which has two inputs 94 and 96. When the first input is actuated by a momentary trigger pulse, driver transistor 82 is turned on. When input 96 is energized, the driver transistor is turned ott.

Many suitable flip-flop units are known in the art and a detailed description of one is not necessary here.

The above description is given in illustration and not in limitation of the invention. Various changes or m-odifications in the embodiment described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth.

I claim:

1. An improved electromagnet dual drive arrangement comprising a first electromagnet and a second electromagnet spaced closely apart, an element movable against one then the other electromagnet into one then another drive condition, said element having a ferromagnetic part which is magnetizable and engageable in intimate zero air-gap contact by either electromagnet, and circuit means to energize said electromagnets with currents to move said element on command into engagement with either one of said electromagnets, said circuit including first switch means to energize one electromagnet with current and second switch means to simultaneously deenergize the other electromagnet for a time long enough to permit said element to shift toward said energized electromagnet, and vice versa, first capacitor means shunting said first switch means to provide a reverse path for discharge of current from said first electromagnet, and second capacitor means shunting said second switch means to provide a reverse path for discharge of current from said second electromagnet, said switch means being simultaneously controllable in opposite phases by an electric signal, whereby the time of shifting said element from one electromagnet to the other is very short and the magnetic holding and shifting forces acting on said element are very high.

2. The arrangement in claim 1 wherein a north pole of said first electromagnet is opposite a north pole of said second electromagnet whereby the magnetism in said element is not reversed when it is shifted from one electromagnet and against the other.

3. The arrangement in claim 1 wherein said element is shiftably carried by a non-magnetic member between said electromagnets, the faces of said element which engage said electromagnets having a friction lining and a raised portion of bare magnetic metal engageable with a respective electromagnet.

4. A high speed, high torque, low wear dual drive arrangement comprising a first electromagnet and a second electromagnet spaced closely apart, a plurality of magnetic segments carried by a non-magnetic rotatable member between said electromagnets, said elements having bare metal portions which are engageable respectively by said electromagnets with zero air-gap, first transistor means to energize said first electromagnet, second transistor means to energize said second electromagnet, first capacitor means shunting said first transistor means and providing a reverse resonant discharge path for current from said first electromagnet, second capacitor means shunting said second transistor means and providing a reverse resonant discharge path for current from said second electromagnet, flip-flop means for turning said first transistor means on and simultaneously turning said second transistor means off, and vice versa, and means to mechanically rotate at least one of said electromagnets.

5. The arrangement in claim 4 wherein said electromagnets have hardened faces, and said elements are of relatively soft iron with brake lining material partly covering their faces.

6. The arrangement in claim 1 wherein each electro-- magnet has a circular face with a narrow annular magnetic gap near the rim of said face, said movable element and said electromagnet faces being engageable with each other with zero air-gap contact across a narrow zone on each side of said annular gap, and brake lining material separating said element and said electromagnet faces adjacent each side of said narrow zone.

(References on following page) 5 6 References Cited by the Examiner 2,958,406 11/ 1960 Pierce 192-107 UNITED STATES PATENTS g venv Leinlnger 61131 Greenblatt 2; $32 13 1 23 5 3,141,530 7/1964 Morley 317-148.5 x 21924314 2/1960 Shepard 192-182 DON WAITE Pfimary Examine- 2,946,418 7/ 1960 Lees-0n 192-182 X DAVID J. WILLIAMOWSKY, Examiner. 

1. AN IMPROVED ELECTROMAGNET DUAL DRIVE ARRANGEMENT COMPRISING A FIRST ELECTROMAGNET AND A SECOND ELECTROMAGNET SPACED CLOSELY APART, AN ELEMENT MOVABLE AGAINST ONE THEN THE OTHER ELECTROMAGNET INTO ONE THEN ANOTHER DRIVE CONDITION, SAID ELEMENT HAVING A FERROMAGNETIC PART WHICH IS MAGNETIZABLE AND ENGAGEABLE IN INTIMATE ZERO AIR-GAP CONTACT BY EITHER ELECTROMAGNET, AND CIRCUIT MEANS TO ENERGIZE SAID ELECTROMAGNETS WITH CURRENTS TO MOVE SAID ELEMENT ON COMMAND INTO ENGAGEMENT WITH EITHER ONE OF SAID ELECTROMAGNETS, SAID CIRCUIT INCLUDING FIRST SWITCH MEANS TO ENERGIZE THE ELECTROMAGNET WITH CURRENT AND SECOND SWITCH MEANS TO SIMULTANEOUSLY DEENERGIZE THE OTHER ELECTROMAGNET FOR A TIME LONG ENOUGH TO PERMIT SAID ELEMENT TO SHIFT TOWARD SAID ENERGIZED ELECTROMAGNET, AND VICE VERSA, FIRST CAPACITOR MEANS SHUNTING SAID FIRST SWITCH MEANS TO PROVIDE A REVERSE PATH FOR DISCHARGE OF CURRENT FROM SAID FIRST ELECTROMAGNET, AND SECOND CAPACITOR MEANS SHUNTING SAID SECOND SWITCH MEANS TO PROVIDE A REVERSE PATH FOR DISCHARGE OF CURRENT FROM SAID SECOND ELECTROMAGNET, SAID SWITCH MEANS BEING SIMULTANEOUSLY CONTROLLABLE IN OPPOSITE PHASES BY AN ELECTRIC SIGNAL, WHEREBY THE TIME OF SHIFTING SAID ELEMENT FROM ONE ELECTROMAGNET TO THE OTHER IS VERY SHOFT AND THE MAGNETIC HOLDING AND SHIFTING FORCES ACTING ON SAID ELEMENT ARE VERY HIGH. 